1. Field of the Invention
The present invention relates to a lighting device used for a computer device, a mobile telephone, or a general electronic device and a display device using the lighting device.
2. Description of the Related Art
In recent years, there is increasingly growing concern about a thin type, light weight, a high intensity, and low power consumption in a color liquid crystal display device used for a computer device, a mobile telephone, or the like. With this concern, a high intensity LED having high light emission efficiency has been used as a light source for the lighting device of the color liquid crystal display device in many cases. A light guide plate for confining light from the light source and irradiating the liquid crystal display device with the confined light has been actively designed in view of a point light source such as an LED. More specifically, there have been disclosed the following technique and structure (for example, see JP 3151830 B). In the technique, light output efficiency is improved by arranging diffusion pattern elements which are formed on the lower surface of a light guide plate and have an orientation in a longitudinal direction, such that the longitudinal direction becomes substantially perpendicular to a direction joining the diffusion pattern element with the light source. In the structure, an oblique portion is provided in a ½ region of the light guide plate so as to prevent an affect of a diffusion pattern element density on an intensity characteristic from saturating.
In the above-mentioned conventional lighting device, the longitudinal direction of the diffusion pattern element is substantially perpendicular to the direction joining the diffusion pattern element with the light source. Therefore, there is a problem in that an arrangement density of the diffusion pattern elements to an arc direction about the diffusion pattern element cannot be sufficiently secured and thus the pattern arrangement becomes difficult. In addition, when the oblique portion is provided in substantially ½ region of the light guide plate, a reflection angle of light multi-reflected in an inner part of the oblique portion is changed with transmission of the light. Therefore, the diffusion pattern element is hard to design.